1. Field of the Invention
This invention in one embodiment relates to a method for contact bonding of lactam-polyol-polyacyl lactam or acyl-polylactam terpolymers as melt blends of said terpolymers with polyamides in filament forms by means of amorphous state contacting to achieve the bonding to an integral web. This is preferably followed by crystallization of the contacted fibers. The invention thus relates to a method for producing non-woven webs having autogenous, crossing point bonding of the individual fibers or filaments at temperatures of up to 210.degree. C. and preferably 20.degree. C. to 210.degree. C.
In yet another aspect, this invention relates to the above contact bonding of lactam terpolymers and/or melt blends of said terpolymers with polyamides in the presence of water, followed by drying and crystallization while the fibers are in contact with one another.
In the above embodiment of this invention there is a retardation of crystallization of nascent, amorphous fibers of the melt blends of said block terpolymers with polyamides, said retardation of crystallization resulting from the presence of the polyol portion of the terpolymer.
However, in the embodiment of this invention with non-nascent, e.g., crystallized fibers, similar non-woven fabrics of excellent drapeability are obtained when such melt blended fibers are contacted under thermal bonding conditions such as 200.degree. C. to 250.degree. C.
In the present description, the term melt blend refers to a combination of polymers such as polyamide together with a lactam terpolymer which are melted together for fiber extrusion or other processing. Thus a mixture of the ground powders or pellets of the respective polymers are melted, for example, in an extruder, and after passage through the extruder screw are passed into fiber or film dies or into molds for the production of shaped articles.
2. Description of the Prior Art
The fibers or filaments comprising a non-woven fabric have in the past been bonded by the use of external binders or by softening the fibers with heat, solvent or plasticizer and subjecting them to substantial pressure while in the softened state. The external binder may be an adhesive substance which is cured after the application thereof or it may be rendered adhesive after application by use of heat, solvent or plasticizer. External binders may be applied as powders, solutions, emulsions or even in the form of fibers; however, these methods suffer from several disadvantages. The use of an outside binder presents problems in uniform applications and limits the properties of the entire web to those of the binder. Thus, for example, if a fiber with a relatively low melting point is used as a bonding material, the temperature conditions to which the web or resulting fabric may be subjected, are limited by the melting point of the binder fibers.
Solvent bonding of the previous methods is not easily controlled and frequently tends to alter the aesthetic properties of the web. For example, achieving adequate adhesiveness in the filaments without dissolving the entire web or at least impairing the physical properties thereof is difficult. Furthermore, the intersections at which the filaments are bonded frequently have a swollen appearance which evidences the solution and redeposition of polymer which is referred to as polymer migration. In most instances, these swollen areas around the bonds do not possess the same dye acceptance level because of changes in the crystalline structure which is localized at the bonds sites thereby causing non-uniform dyeing.
Because of the low cost of non-wovens, continued work is progressing to produce fabrics which have the lower cost of non-woven fabrics, while achieving the properties of woven fabrics. Non-woven fabrics commonly are made by mixing fibers of staple length and depositing the fibers as a continuous sheet or web. The fibers in web form are then bonded together, for example, by the application of various known binders or binding techniques such as thermal or pressure means. The binding means is selected in order to give good bonding to a variety of different fibers so uniform bonding throughout the web will be achieved. To obtain a fabric with reasonable strength, it has been necessary to employ substantial proportions of adhesive binders, substantial pressure or heat and the like; however, the high concentration of binders, excessive pressure or heat produce fabrics which are stiff rather than soft and supple due to the low degree of movement or slip between the individual fibers of the resulting fabrics.
To improve the hand of non-woven fabrics, it has been proposed to apply new bonding techniques which achieve improved hand while maintaining strength properties. It has been suggested to employ adhesive bondings which are rubbery or plastic in nature so that bonding extensibility will be achieved through the deformation of the binder at the point of contact between fibers. This approach has resulted in limited improvement in hand of the fabric; however, it has not been totally successful in matching the characteristics of woven fabrics in non-wovens.
Contact bonding of the nascent nylon 66 fibers fails to occur since nylon 66 crystallizes very rapidly.